Process for producing an anionic clay-containing composition

ABSTRACT

This patent describes an economical and environment-friendly continuous process for the synthesis of anionic clay-containing compositions. It involves reacting a slurry comprising aluminium trihydrate and/or its calcined form, with a magnesium source. There is no necessity to wash or filter the product. It can be spray dried directly to form microspheres or can be extruded to form shaped bodies. The product can be combined with other ingredients in the manufacture of catalysts, absorbents, pharmaceuticals, cosmetics, detergents, and other commodity products.

This is a Continuation-in-Part of application Ser. No. 09/021,839 filedFeb. 11, 1998 now abandoned. The entire disclosure of the priorapplication(s) is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

This invention involves the preparation of anionic clays and thepreparation of Mg—Al solid solutions by heat-treatment of the anionicclay. Anionic clays have a crystal structure which consists ofpositively charged layers built up of specific combinations of metalhydroxides between which there are anions and water molecules.Hydrotalcite is an example of a naturally occurring anionic clay, inwhich carbonate is the predominant anion present. Meixnerite is ananionic clay wherein hydroxyl is the predominant anion present.

In hydrotalcite-like anionic clays the brucite-like main layers arebuilt up of octahedra alternating with interlayers in which watermolecules and anions, more particularly carbonate ions, are distributed.The interlayers may contain anions such as NO₃ ⁻, OH, Cl⁻, Br⁻, I⁻, SO₄²⁻, SiO₃ ²⁻, CrO₄ ²⁻, BO₃ ²⁻, MnO₄ ⁻, HGaO₃ ²⁻, HVO₄ ²⁻, ClO₄ ⁻, BO₃ ²⁻,pillaring anions such as V₁₀O₂₆ ⁻⁶ and Mo₇O₂₄ ⁶⁻. monocarboxylates suchas acetate, dicarboxylates such as oxalate, alkyl sulphonates such aslaurylsulphonate.

It should be noted that a variety of terms are used to describe thematerial which is referred to in this patent as an anionic clay.Hydrotalcite-like and layered double hydroxide are interchangeably usedby those skilled in the art. In this patent application we refer to thematerials as anionic clays, comprising within that termhydrotalcite-like and layered double hydroxide materials.

The preparation of anionic clays has been described in many prior artpublications.

Recently, two major reviews of anionic clay chemistry were published inwhich the synthesis methods available for anionic clay synthesis havebeen summarized, F. Cavani et al “Hydrotalcite-type anionic clays:Preparation, Properties and Applications,” Catalysis Today”, 11 (1991)Elsevier Science Publishers B. V. Amsterdam.

J P Besse and others “Anionic clays:trends in pillary chemistry, itssynthesis and microporous solids” (1992), 2, 108, editors: M. I.Occelli, H. E. Robson, Van Nostrand Reinhold, N. Y.

In these reviews the authors state that a characteristic of anionicclays is that mild calcination at 500° C. results in the formation of adisordered MgO-like product. Said disordered MgO-like product isdistinguishable from spinel (which results upon severe calcination) andfrom anionic clays. In this patent application we refer to saiddisordered MgO-like materials as Mg—Al solid solutions. Furthermore,these Mg—Al solid solutions contain a well-known memory effect wherebythe exposure to water of such calcined materials results in thereformation of the anionic clay structure

For work on anionic clays, reference is given to the following articles:

Helv. Chim. Acta, 25, 106-137 and 555-569 (1942)

J. Am. Ceram. Soc., 42, no. 3, 121 (1959)

Chemistry Letters (Japan), 843 (1973)

Clays and Clay Minerals, 23, 369 (1975)

Clays and Clay Minerals, 28, 50 (1980)

Clays and Clay Minerals, 34, 507 (1996)

Materials Chemistry and Physics, 14, 569 (1986).

In addition there is an extensive amount of patent literature on the useof anionic clays and processes for their preparation

European Patent Application 0 536 879 describes a method for introducingpH-dependent anions into the clay. The clay is prepared by the additionof a solution of Al(NO₃)₃ and Mg(NO₃)₂ to a basic solution containingborate anions. The product is then filtered, washed repeatedly withwater, and dried overnight. Additionally mixtures of Zn/Mg are used.

In U.S. Pat. No. 3,796,792 by Miyata entitled “Composite MetalHydroxides” a range of materials is prepared into which an extensiverange of cations is incorporated, including Sc, La, Th, In, etc. In theexamples given solutions of the divalent and trivalent cations areprepared and mixed with base to cause co-precipitation. The resultingproducts are filtered, washed with water, and dried at 80° C. Example 1refers to Mg and Al and Example 2 to Mg and Bi. Other examples aregiven, and in each case soluble salts are used to make solutions priorto precipitation of the anionic clay at high pH.

In U.S. Pat. No. 3,879,523 by Miyata entitled “Composite MetalHydroxides” also a large number of preparation examples is outlined. Theunderlying chemistry, however, is again based on the co-precipitation ofsoluble salts followed by washing and drying. It is important toemphasize that washing is a necessary part of such preparations, becauseto create a basic environment for co-precipitation of the metal ions abasic solution is needed and this is provided by NaOH/Na₂CO₃ solutions.Residual sodium, for example, can have a significant deleterious effecton the subsequent performance of the product as a catalyst or oxidesupport.

In U.S. Pat. No. 3,879,525 (Miyata) very similar procedures are againdescribed.

In U.S. Pat. No. 4,351,814 to Miyata et al. a method for making fibroushydrotalcite is described. Such materials differ in structure from thenormal plate-like morphology. The synthesis again involves solublesalts. For example, an aqueous solution of a mixture of MgCl₂ and CaCl₂is prepared and suitably aged. From this a needle-like productMg₂(OH)₃Cl.4H₂O precipitates. A separate solution of sodium aluminate isthen reacted in an autoclave with the solid Mg₂(OH)₃Cl.4H₂O and theproduct is again filtered, washed with water, and dried.

In U.S. Pat. No. 4,458,026 to Reichle, in which heat-treated anionicclays are described as catalysts for aldol condensation reactions, againuse is made of magnesium and aluminum nitrate salt solutions. Suchsolutions being added to a second solution of NAOH and Na₂CO₃. Afterprecipitation the slurry is filtered and washed twice with distilledwater before drying at 125° C.

In U.S. Pat. No. 4,656,156 to Misra the preparation of a novel absorbentbased on mixing activated alumina and hydrotalcite is described. Thehydrotalcite is made by reacting activated MgO (prepared by activating amagnesium compound such as magnesium carbonate or magnesium hydroxide)with aqueous solutions containing aluminate, carbonate and hydroxylions. As an example the solution is made from NAOH, Na₂CO₃ and Al₂O₃. Inparticular, the synthesis involves the use of industrial Bayer liquor asthe source of Al. The resulting products are washed and filtered beforedrying at 105° C.

In U.S. Pat. No. 4,904,457 to Misra a method is described for producinghydrotalcites in high yield by reacting activated magnesia with anaqueous solution containing aluminate, carbonate, and hydroxyl ions.

The methodology is repeated in U.S. Pat. No. 4,656,156.

In U.S. Pat. No. 5,507,980 to Kelkar et at al. a process is describedfor making novel catalysts, catalyst supports, and absorbers comprisingsynthetic hydrotalcite-like binders. The synthesis of the typical sheethydrotalcite involves reacting pseudo-boehmite to which acetic acid hasbeen added to peptize the pseudo-boehmite. This is then mixed withmagnesia. More importantly, the patent summary states clearly that theinvention uses mono carboxylic organic acids such as formic, propionicand isobutyric acid. In this patent the conventional approaches topreparing hydrotalcite are presented.

In U.S. Pat. No. 5,439,861 a process is disclosed for preparing acatalysts for synthesis gas production based on hydrotalcite. The methodof preparation is again based, on the co-precipitation of soluble saltsby mixing with base, for example, by the addition of a solution ofRhCl₃, Mg(NO₃)₂ and Al(NO₃)₃ to a solution of Na₂CO₃ and NaOH.

Also in U.S. Pat. No. 5,399,537 to Bhattacharyya in the preparation ofnickel-containing catalysts based on hydrotalcite use is made of theco-precipitation of soluble magnesium and aluminum salts.

In U.S. Pat. No. 5,591,418 to Bhattacharyya a catalyst for removingsulphur oxides or nitrogen oxides from a gaseous mixture is made bycalcining an anionic clay, said anionic clay having been prepared byco-precipitation of a solution of Mg(NO₃)₂, Al(NO₃)₃ and Ce(NO₃)₃. Theproduct again is filtered and repeatedly washed with de-ionized water.

In U.S. Pat. No. 5,114,898/WO 9110505 Pinnavaia et al. describe layereddouble hydroxide sorbents for the removal of sulphur oxide(s) from fluegases, which layered double hydroxide is prepared by reacting a solutionof Al and Mg nitrates or chlorides with a solution of NAOH and Na₂CO₃.In U.S. Pat. No. 5,079,203/WO 9118670 layered double hydroxidesintercalated with polyoxo anions are described, with the parent claybeing made by co-precipitation techniques.

In U.S. Pat. No. 5,578,286 in the name of Alcoa a process for thepreparation of meixnerite is described. The meixnerite may be contactedwith a dicarboxylate or polycarboxylate anion to form ahydrotalcite-like material. In comparative examples 1-3 hydromagnesiteis contacted with aluminum trihydrate in a CO₂ atmosphere, greater than30 atmospheres. No hydrotalcite was obtained in these examples.

In U.S. Pat. No. 5,514,316 a method for the preparation of meixnerite isdescribed using magnesium oxide and transition alumina. For comparativepurposes aluminum trihydrate was used in combination with magnesiumoxide. It was indicated that this method did not work as well as withtransition alumina.

U.S. Pat. No. 4,454,244 and U.S. Pat. No. 4,843,168 describe the use ofpillaring anions in anionic clays.

In U.S. Pat. No. 4,946,581 and U.S. Pat. No. 4,952,382 to van Broekhovenco-precipitation of soluble salts such as Mg(NO₃)₂ and Al(NO₃)₃ with,and without the incorporation of rare earth salts was used for thepreparation of anionic clays as catalyst components and additives. Avariety of anions and di- and tri-valent cations are described.

As indicated in the description of the prior art given-above, there aremany applications of anionic clays.

These include but are not restricted to: catalysts, adsorbents, drillingmuds, catalyst supports and carriers, extenders and applications in themedical field. In particular van Broekhoven has described their use inSO_(x) abatement chemistry.

Because of this wide variety of large-scale commercial applications forthese materials, new processes utilizing alternative inexpensive rawmaterials and which can be carried out in continuous mode are needed toprovide a more cost-effective and environmentally compatible processesfor making anionic clays. In particular, from the prior art describedabove one can conclude that the preparation process can be improved inthe following ways: the use of cheaper sources of reactants, processesfor easier handling of the reactants, so that there is no need forwashing or filtration, eliminating the filtration problems associatedwith these fine-particled materials, the avoidance of alkali metals(which can be particularly disadvantageous for certain catalyticapplications): In prior art preparations organic acids were used topeptize alumina. The use of organic acids is expensive and introduces anadditional step in the synthesis process and is therefore notcost-effective. Further, in drying or calcining the anionic clayprepared by prior art processes gaseous emissions of nitrogen oxides,halogens, sulphur oxides, etc. are encountered which cause environmentalpollution problems.

SUMMARY OF THE INVENTION

Our invention includes a process for producing anionic clay-containingcompositions using raw materials which are inexpensive and utilizingsuch raw materials in a simple process which is extremely suitable to becarried out in continuous mode. The process involves reacting mixtureswith or without stirring in water at ambient or elevated temperature atatmospheric or elevated pressure. Such continuous processes can beoperated in standard industrial equipment. More specifically, there isno need for washing or filtering, and a wide range of ratios of Mg/Al inthe reaction product is possible.

In the process according to the invention an aluminum source and amagnesium source, for instance magnesium oxide or brucite, reacted inaqueous suspension to obtain an anionic clay and unreacted asource-containing composition. This invention involves the use ofaluminum trihydrate (such as gibbsite, bayerite or nordstrandite) orthermally treated forms thereof as aluminum source. The reaction iscarried out at ambient or elevated temperature and ambient or elevatedpressure and the reaction mixture results in the direct formation of ananionic clay which can be obtained by simply drying the slurrycontinuously retrieved from the reactor. The powder X-ray diffractionpattern (PXRD) suggests that the product is comparable to anionic claysmade by other standard (batch) methods. The physical and chemicalproperties of the product are also comparable to those anionic claysmade by the other conventional methods. The overall process of thisinvention is very flexible, enabling a wide variety cf anionicclay-containing compositions and anionic clay-like materials involvingfor example carbonate, hydroxide and other anions to be prepared in aneconomically and environmental-friendly manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a PXRD pattern of commercially available Mg—Al carbonateanionic clay.

FIG. 2 shows a PXRD pattern of a Mg—Al carbonate anionic clay preparedby coprecipitation.

FIG. 3 shows a PXRD pattern of a Mg—Al anionic clay-containingcomposition prepared by the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention involves the preparation of an anionic clay-containingcomposition. In particular it describes a process for the preparation ofan anionic clay-containing composition wherein an aluminum source and amagnesium source are reacted in aqueous suspension to obtain an anionicclay and unreacted aluminum source-containing composition, the aluminumsource being aluminum trihydrate or its thermally treated forms. Themagnesium source may be composed of a solution of a magnesium salt, asolid magnesium-bearing compound or a mixture of the two. Reactionbetween the Mg source and aluminum trihydrate or its thermally treatedform results in the direct formation of an anionic clay. In the processaccording to the invention part of the aluminum source remains unreactedand ends up in the anionic clay-containing composition. The reactiontakes place at room temperature or higher. At temperatures higher than100° C., the reaction is preferably carried out under autogeneousconditions. In the method according to the invention carbonate,hydroxyl, or other anions or mixtures thereof, either provided withinthe reaction medium for example by feeding a soluble salt to the reactoror absorbed during the synthesis from the atmosphere, are incorporatedinto the interlayer region as the necessary charge-balancing anion.

Anionic clays prepared by this method exhibit the well known propertiesand characteristics (e.g. chemical analysis, powder X-ray diffractionpattern, FTIR, thermal decomposition characteristics, surface area, porevolume, and pore size distribution) usually associated with anionicclays prepared by the customary and previously disclosed methods.

Upon being heated, anionic clays generally form Mg—Al solid solutions,and at higher temperatures, spinels. When used as a catalyst, anadsorbent (for instance a SO_(x) adsorbent for catalytic crackingreactions), or a catalyst support, the anionic clay according to theinvention is usually heated during preparation and is thus in the Mg—Alsolid solution form. During use in a FCC unit, the catalyst or adsorbentis converted from an anionic clay into Mg—Al solid solutions.

Therefore, the present invention is also directed to a process whereinan anionic clay-containing composition prepared by the process accordingto the invention, is heat-treated at a temperature between 300 and 1200°C. to form a Mg—Al-containing solid solution and/or spinel-containingcomposition.

The anionic clay in the composition according to the invention has alayered structure corresponding to the general formula

[Mg_(m) ²⁻Al_(n) ³⁺(OH)_(2m+2n).](X_(n/z) ²⁻).bH₂O

Wherein m and n have a value such that m/n=1 to 10, preferably 1 to 6,and b has a value in the range of from 0 to 10, generally a value of 2to 6 and often a value of about 4. X may be CO₃ ²⁻, OH⁻ or any otheranion normally present in the interlayers of anionic clays. It is morepreferred that m/n should have a value of 2 to 4, more particularly avalue close to 3.

Since the present process does not require washing of the product orfiltering, there is no filtrate waste or gaseous emissions (e.g. fromacid decomposition), making the process particularlyenvironmental-friendly and more suited to the environmental constraintswhich are increasingly imposed on commercial operations The product canbe spray dried directly to. form microspheres or can be extruded to formshaped bodies.

Aluminium source

The present invention includes the use of crystalline aluminumtrihydrate (ATH), for example gibbsites provided by Reynolds AluminumCompany RH-20® or JM Huber Micral® grades. Also BOC (Bauxite OreConcentrate), bayerite and nordstrandite are suitable aluminiumtrihydrates. BOC is the cheapest alumina source. The alumina trihydrateis preferred to have a small particle size. In another embodiment of theinvention thermally treated forms of gibbsite are used. Combinations ofaluminum trihydrate and thermally treated forms of aluminum trihydratecan also be used. The calcined aluminum trihydrate is readily obtainedby thermally treating aluminum trihydrate (gibbsite) at a temperatureranging from 100 to 800° C. for 15 minutes to 24 hours. In any event,the calcining temperature and time for obtaining calcined aluminumtrihydrate should be sufficient to cause a measurable increase of thesurface area in view of the surface area of the gibbsite as produced bythe Bayer process which is generally between 30 and 50 m²/g. It shouldbe noted that within the concept of this invention flash calcinedalumina is also considered to be a thermally treated form of aluminumtrihydrate, although generally it is considered a very specific alumina.Flash calcined alumina is obtained by treating aluminum trihydrate attemperatures between 800-1000° C. for very short periods of time inspecial industrial equipment, as is described in U.S. Pat. No. 4,051,072and U.S. Pat. No. 3,222,129. Combinations of various thermally treatedforms of aluminum trihydrate can also be used. Preferably the aluminumsource is fed to the reactor in the form of a slurry. In particular weemphasize that there is no need to use a peptizable alumina source(gibbsite is not peptizable) and as a result no need to add eithermineral or organic acid to vary the pH of the mixture. As mentionedabove, in the present invention part of the aluminum trihydrate or itsthermally form remains unreacted and ends up in the resulting anionicclay-containing composition. In the process according to our inventionother aluminum sources beside aluminum trihydrate or its thermallytreated forms may be added to the aqueous suspension such as oxides andhydroxides of aluminum, (e.g. sols, flash calcined alumina, gels,pseudo-boehmite, boehmite) aluminum salts such as aluminum nitrate,aluminium chloride, aluminium chlorohydrate and sodium aluminate. Theother aluminum sources may be soluble or insoluble in water and may beadded to the aluminum trihydrate and/or its thermally treated form or itmay be added to the aqueous suspension separately as a solid, a solutionor as a suspension.

Magnesium source

Mg-bearing sources which may be used include MgO, Mg(OH)₂, magnesiumacetate, magnesium formate, magnesium hydroxy acetate, hydromagnesite(Mg₃(CO₃)₄(OH)₂), magnesium carbonate, magnesium bicarbonate, magnesiumnitrate, magnesium chloride, dolomite and sepiolite. Both solid Mgsources and soluble Mg salts are suitable. Also combinations of Mgsources may be used. The magnesium source may be added to the reactor asa solid, a solution, or, preferably, as a slurry. The magnesium sourcemay also be combined with the aluminum source before it is added to thereactor.

Conditions

Because of its simplicity, this process is particularly suitable to becarried out in a continuous mode. Thereto an aluminum source and amagnesium source are fed to a reactor and reacted in aqueous suspensionto obtain an anionic clay-containing composition. In the case of a batchprocess an aluminum source and a magnesium source are added to a reactorand reacted in aqueous suspension to obtain an anionic clay-containingcomposition. Within the context of this invention a reactor isconsidered to be any confined zone in which the reaction between thealuminum source and magnesium source takes place. The reactor may beequipped with stirrers, baffles etcetera to ensure homogeneous mixing ofthe reactants. The reaction can take place with or without stirring, atambient or at elevated temperature and at atmospheric or elevatedpressure. Usually, a temperature between 0 and 100° C. is used at orabove atmospheric pressure. It is preferred to carry out the process attemperatures above 50° C. rather than at room temperature, because thisresults in anionic clays with sharper peaks in the x-ray diffractionpattern than anionic clay-containing compositions obtained at roomtemperature. The reactor may be heated by any heating source such as afurnace, microwave, infrared sources, heating jackets (either electricalor with a heating fluid), lamps, etcetera.

The aqueous suspension in the reactor may be obtained by either addingslurries of the starting materials, either combined or separate, to thereactor or adding magnesium source to a slurry of alumina trihydrateand/or its calcined form or vice versa and adding the resulting slurryto the reactor. It is possible to treat, for instance the aluminumtrihydrate slurry at elevated temperature and then add either the Mgsource per se, or add the Mg source in a slurry or solution either tothe reactor or the aluminium source slurry. Given particular facilitieswhich might be available, the continuous process can be conductedhydrothermally. This is particularly advantageous, because it this isfaster and a higher conversion is obtained. There is no need to wash orfilter the product, as unwanted ions (e.g. sodium, ammonium, chloride,sulphate) which are frequently encountered when using other preparationmethods, are absent in the product.

In a further embodiment of the invention, the process is conducted in amulti-step process, e.g. a slurry of ATH and Mg source is treatedthermally in a first reactor at a mild temperature, followed by ahydrothermal treatment in a second reactor. If desired a preformedanionic clay may be added to the reactor. The preformed clay may berecycled anionic clay from the reaction mixture or anionic clay madeseparately by the process according to the invention or any otherprocess.

If desired, organic or inorganic acids and bases, for example forcontrol of the pH, may be fed to the reactor or added to either themagnesium source or the aluminum source before they are fed to thereactor. An example of a preferred pH modifier is an ammonium base,because upon drying no deleterious cations remain in the anionic clay.

If desired, the anionic clay-containing composition prepared by theprocess according to the invention may be subjected to ion exchange.Upon ion exchange the interlayer charge-balancing anions are replacedwith other anions. The other anions are the ones commonly present inanionic clays and include pillaring anions such as V₁₀O₂₆ ⁻⁶, Mo₇O₂₄ ³⁻,PW₁₂O₄₀ ³⁻, B(OH)₄ ⁻, B₄O₅(OH)₄ ²⁻, HBO₄ ²⁻, HGaO₃ ²⁻, CrO₄ ²⁻. Examplesof suitable pillaring anions are given in U.S. Pat. No. 4,774,212 whichis included by reference for this purpose. The ion exchange can beconducted before or after drying the anionic clay and aluminumsource-containing composition formed in the slurry.

The process of the invention provides wide flexibility in preparingproducts with a wide range of Mg:Al ratios. The Mg:Al ratio can varyfrom 0.1 to 10, preferably from 1 to 6, more preferred from 2 to 4, andespecially preferred to close to 3.

For some applications it is desirable to have additives, both metals andnon-metals, such as rare earth metals, Si, P, B, group VI, group VIII,alkaline earth (for instance Ca and Ba) and/or transition metals (forexample Mn, Fe, Ti, Zr, Cu, Ni, Zn, Mo, Sn), present. The metals andnon-metals can easily be deposited on the anionic clay or the solidsolution according to the invention or they can be added either to thealumina source or magnesium source which are added to the reactor oradded the reactor separately. Suitable sources of metals or non-metalsare oxides, halides or any other salt such as chlorides, nitratesetcetera. In the case of a multi-step process the metals and non-metalsmay be added in any of the steps. Is can be especially advantageous forcontrolling the distribution of the metals and non-metals in the anionicclay.

As mentioned above, in the present invention part of the aluminumtrihydrate or its thermally form remains unreacted and ends up in theresulting anionic clay-containing composition. The resulting compositioncan advantageously used as an absorbent or as a catalyst additive ormatrix. The composition already contains aluminum trihydrate or itsthermally treated form which acts as a binder for the anionic clay inthe composition. Therefore, the present invention is also directed tothe anionic clay-containing composition prepared by the process of theinvention.

The present invention is illustrated by the following examples which arenot to be considered limitative by any means.

EXAMPLES

Comparative Examples Based on the State of the Art

Comparative Example 1

A commercially available sample of a Mg—Al carbonate anionic clay wasobtained from Reheis Chemical Company. Its PXRD pattern is shown forillustration in FIG. 1.

D(A) 7.80 3.89 2.59 I/I₀ 100 40 35

Comparative Example 2

This comparative example illustrates the co-precipitation method whereMg and Al salt solutions are added to a solution of base. (U.S. Pat. No.3,979,523 Assignee Kyowa Chemical Industry, Japan).

A solution containing 0.04 M Of Al(NO₃)₂.9H₂Oand 0.08 M Of Mg(NO₃)₂.6H₂Oin 100 ml distilled water was added dropwise and with vigorous stirringto 150 ml of distilled water containing 0.05 M of Na₂CO₃ at roomtemperature. Mg/Al ratio of 20. The pH was maintained close to 10 by theaddition of 3N NAOH and the resulting slurry aged overnight at roomtemperature. The precipitate was separated by centrifuge, washed severaltimes with hot distilled water then dried at 65° C. overnight.

The PXRD pattern obtained from this sample is shown in FIG. 2. Theresults were:

D(A) 7.84 3.90 2.56 I/I₀ 100 40 20

Thermogravimetric analysis showed three weight losses: at approximately100, 250 and 450° C. which are ascribed to loss of physisorbed water,interlayer water and loss of CO₂ and lattice dehydroxylation.

Comparative Example 3

The product obtained from Example 1 was calcined at 500° C. for 12 h.The product gave broad X-ray diffraction lines at 45 and 63 degrees twotheta similar to those obtained for samples of calcined anionic claysprepared by other established methods with a Mg:Al ratio between 2 and5.

Comparative Example 4

The product obtained from Example 2 was calcined at 500° C. for 12 h.The product gave broad X-ray diffraction lines at 45 and 63 degrees twotheta similar to those obtained for samples of calcined anionic claysprepared by other established methods with a Mg:Al ratio between 2 and5.

Comparative Example 5

0.15 g of the product from Comparative Example 3 was added to 75 mlwater at room temperature and stirred for 12 h. The product wasfiltered, washed and dried at 80° C. The PXRD pattern indicated that theanionic clay structure had reformed with characteristic lines at 11.5,23.5 and 35° in the PXRD.

Comparative Example 6

0.15 g of the product from Example 4 was added to water at roomtemperature and stirred for 12 h. The product was filtered and dried at80° C. The PXRD pattern indicated that the product was similar to thatfor Comparative Example 5 and confirmed that the anionic clay structurehad reformed.

Examples of This Invention

The anionic clays may be prepared under nitrogen or carbondioxide-freeatmosphere, so that the anionic clay predominantly comprises hydroxiderather than pre dominantly carbonate as charge balancing anion. It isalso possible to feed carbon dioxide to the reactor so that an anionicclay results with predominantly carbonate as charge balancing anion.

The following examples illustrate either the use of a Gibbsite (Micral916®) obtained from J M Huber as a source of alumina or the use of BOC.

Example 7

3.92 g of MgO was suspended in 50 cl of de-ionized water at 65° C. in abeaker in an air atmosphere. 3 g of Micral-916 Gibbsite was then addedand the mixture kept at 65° C. overnight. The resulting product was thendried in air at 65° C. overnight. The product consisted of a mixture ofa carbonate-containing anionic clay and unreacted Gibbsite (FIG. 3).

Example 8

3.92 g of MgO was suspended in 50 cl of de-ionized water at 65° C. in abeaker in an air atmosphere. 3 g of Micral-916 Gibbsite was then addedand the mixture kept at 90° C. for 24 h. The resulting product was thendried in air at 65° C. overnight. The product consisted of a mixture ofa carbonate-containing anionic clay and unreacted Gibbsite.

Example 9

3.92 g of MgO was suspended in 50 cl of de-ionized water at 65° C. in abeaker in an air atmosphere 3 g of Micral-916 Gibbsite was then addedalong with 5 wt % of the product of Example 2 and the mixture kept at65° C. for 24 h. The resulting product was then dried in air at 65° C.overnight. The product consisted of a mixture of a carbonate-conaininganionic clay and unreacted Gibbsite.

Example 10

3.92 g of MgO was suspended in 50 cl of de-ionized water at 65° C. in abeaker in an air atmosphere. 3 g of Micral-916 Gibbsite was then addedalong with 5 wt % of Example 2 and the mixture hydrothermally treated at170° C. for 1 h. The resulting product was then dried in air at 65° C.overnight. The product consisted of a mixture of a carbonate-containinganionic clay and unreacted Gibbsite.

We claim:
 1. A process for the preparation of an anionic clay-containingcomposition, comprising reacting an aluminum source and a magnesiumsource in an aqueous suspension to obtain an anionic clay and anunreacted aluminum source-containing composition, the aluminum sourcebeing at least one of aluminum trihydrate and a thermally treated formof aluminum trihydrate.
 2. The process according to claim 1 wherein thealuminum source is a thermally treated form of aluminum trihydrate. 3.The process according to claim 1, wherein the aluminum source isaluminum trihydrate.
 4. The process according to claim 1 wherein theaqueous suspension further comprises at least one alumina source inaddition to the at least one of aluminum trihydrate and a thermallytreated form of aluminum trihydrate.
 5. The process according to claim 1wherein the magnesium source is at least one of magnesium oxide, Mg(OH)₂and MgCO₃.
 6. The process according to claim 1 wherein the reactiontakes place at a temperature between 0 and 100° C. and at a pressure ator above atmospheric pressure.
 7. The process according to claim 1wherein the reaction takes place at a temperature above 50° C. and at apressure at or above atmospheric pressure.
 8. The process according toclaim 1 wherein the reaction is conducted at a temperature above 100° C.and at a pressure above atmospheric pressure.
 9. The process accordingto claim 1 wherein metals or non-metals are added to at least one of theaqueous suspension, the aluminum source and the magnesium source. 10.The process according to claim 9 wherein the metals or non-metals areadded to the aluminum source.
 11. The process according to claim 9wherein the metals or non-metals are added to the magnesium source. 12.The process according to claim 1 wherein the anionic clay is subjectedto an ion-exchange treatment.
 13. A process according to claim 1 whereinthe anionic clay is ion exchanged with pillaring anions.
 14. The processaccording to claim 13 wherein the pillaring anions are V₁₀O₂₆ ⁶⁻ andMo₇O₂₄ ⁶⁻.
 15. The process according to claim 1 wherein metals ornon-metals are deposited on the anionic clay.
 16. A process for thepreparation of at least one of a Al—Mg-containing solid solution andspinel, comprising heat treating an anionic clay obtained by the processof claim 1 at a temperature between 300 and 1200° C.
 17. An anionicclay-containing composition prepared by the process of claim
 1. 18. Ananionic clay-containing composition comprising aluminum trihydrate or athermally treated form of aluminum trihydrate.